Petroleum coke, or coke, is a byproduct of the petroleum refining process. Coke may be produced using a delayed coking process in which residual oil is heated to its thermal cracking temperature. The delayed coking process utilizes a coke drum in which the heated residual oil is pumped and maintained at high heat and pressure, and then allowed to cool. The delayed coking process is generally carried out over a 24 hour period.
Once the coke has cooled sufficiently, valves on the top and bottom of the coke drum are opened to allow the coke to be removed from the drum Generally, the coke is removed using a high pressure water cutting tool inserted through the top valve to break the coke into pieces that fall out of the drum through the opened bottom valve.
Coke drums are very large, and when full, can contain thousands of tons of coke. Additionally, because coke drums are pressurized during the delayed coking process, the top and bottom valves are designed to have near zero tolerances between the valve components. Because of the enormous weight from the coke combined with the near zero tolerances, a strong actuator is required to operate the valve.
Many prior art unheading valves have been designed to be operated by hydraulic actuators because of their relative strength and reliability. Hydraulic valve actuators, however, suffer from various drawbacks. For example, hydraulic valve actuators, when compared to electric valve actuators, generally require more maintenance, are more complex to install, are more difficult to position, can be less efficient, require a more complex control system, and pose greater environmental concerns. Unfortunately, prior art attempts to design an electric valve actuator for operating an unheading valve of a coke drum have been unsuccessful.